Sorry but I didn't initially interpret your 1st Follow-up as a "that's what I said". But now that you've explained what you meant, I can see what you mean. What threw me was when you wrote: I don't see a need for 12" of insulation in an attic... the insulation only should be as high as the joists, and should not have to be compressed to lay a floor of plywood. My home, in particular, has 12" of BLOWN insulation installed over 10" joists. Sooooo, when JackD explained what happens when 12" of insulation is compressed to the 'thickness' of 6" ceiling joists, I thought it would be reasonable (not necessarily the case) to assume the insulation in his 'example' is blown like mine. (Again, it is just an example and it was an inference I personally made. Blown insulation is still a commonly used form of insulation in an attic, don't ya know.) So when you said you what you said, you took JackD's example (in my mind) as an 'installation' that doesn't need to be done. To which I said 'No' because it IS done when the insulation is of a blown 'consistancy'. Gene's insulation may or may NOT be blown in his house but all one needs to 'understand/realize' is JackD's 'point' about what happens when one compresses attic insulation ESPECIALLY where it' ABOVE the joists (no matter if it's blown or batt.) I guess I took your reply an extra step figuring you didn't know that blown insulation COULD VERY EASILY be installed at a height MUCH higher than the joists themselves, thus, JackD's explanation. As I said, blown insulation is still VERY commonly used today.